Method and device for measuring the position of the edge of a material web

Abstract

A device and method provide for measuring the position of the edge of a material web by illuminating an area of the edge area and detecting shadows cast by the material web. Two or more transmitters arranged in a line transverse to the edge of the material web are used for illumination. A linear sensor also arranged transverse to the edge of the material web is used to sense the locations of the shadows. The position of the edge of the material web is detected from the sensed shadow and the locations of the transmitters and sensors.

1 . A method for measuring a position of an edge of a material web, the method comprising:
 illuminating the edge of the material web by at least two transmitters, where the transmitters are substantially arranged in a line transverse to the edge of the material web;   detecting shadows cast by the edge of the material web on a sensor, where the sensor includes an array of sensor elements substantially arranged in a line transverse to the edge of material web; and   calculating the position of the edge of the material web.   
     
     
         2 . The method of  claim 1 , wherein calculating the position of the edge of the material web comprises utilizing, at least in part, the locations of the detected shadows and the locations of the transmitters and the sensor, and calculating the position of the edge of the material web in the direction between the transmitters and the sensor, the position based at least in part on the difference in the locations of the detected shadows. 
     
     
         3 . The method of  claim 1 , wherein illuminating the edge of the material web by the at least two transmitters and detecting shadows cast by the edge of the material web on the sensor are performed consecutively for each of the at least two transmitters. 
     
     
         4 . The method of  claim 1 , further comprising selected transmitters from an array of transmitters for use in illuminating the edge of the material web by the at least two transmitters. 
     
     
         5 . A device for measuring the position of an edge of a material web, the device comprising:
 at least two transmitters substantially arranged in a line transverse to the edge of the material web;   a sensor having pixels substantially arranged in a line transverse to the edge of material web, where the sensor is configured to sense shadows cast by the material web when illuminated by the transmitters; and   a computing device coupled to the sensor and configured to calculate the position of the edge of the material web from the sensed shadows.   
     
     
         6 . The device of  claim 5 , wherein the at least two transmitters are in a row of transmitters substantially arranged transverse to the edge of the material web, and wherein the computing device is further coupled to the transmitters and is further configured to control which of transmitters in the row of transmitters are activated to calculate the position of the edge of the material web. 
     
     
         7 . The device of  claim 5 , wherein each of the at least two transmitters comprises a light-emitting diode. 
     
     
         8 . The device of  claim 5 , wherein the sensor is selected from the group consisting of a CCD sensor, a CMOS sensor, and a contact image sensor. 
     
     
         9 . The device of  claim 5 , further comprising a semicircular rod arranged as a lens over the sensor and configured to focus light from the at least two transmitters on the sensor. 
     
     
         10 . The device of  claim 5 , further comprising a housing having a U-shaped cross section, wherein the sensor is located in the housing. 
     
     
         11 . The device of  claim 10 , wherein the housing forms at least one light trap by narrowing an opening area over the sensor. 
     
     
         12 . The device of  claim 11 , further comprising a semicircular rod arranged as a lens over the sensor and configured to focus light from the at least two transmitters on the sensor. 
     
     
         13 . The device of  claim 12 , where further comprising a light filter arranged in the housing and configured to suppress ambient light from the sensor. 
     
     
         14 . A device for measuring the position of an edge of a material web, the device comprising:
 at least two transmitters substantially arranged in a line transverse to the edge of the material web; and   a sensor having pixels substantially arranged in a line transverse to the edge of material web, where the sensor is configured to sense shadows cast by the material web when illuminated by the transmitters.   
     
     
         15 . The device of  claim 14 , wherein each of the at least two transmitters comprises a light-emitting diode. 
     
     
         16 . The device of  claim 14 , wherein the sensor is selected from the group consisting of a CCD sensor, a CMOS sensor, and a contact image sensor. 
     
     
         17 . The device of  claim 14 , further comprising a housing having a U-shaped cross section, wherein the sensor is located in the housing. 
     
     
         18 . The device of  claim 17 , wherein the housing forms at least one light trap by narrowing an opening area over the sensor. 
     
     
         19 . The device of  claim 18 , further comprising a semicircular rod arranged as a lens over the sensor and configured to focus light from the at least two transmitters on the sensor. 
     
     
         20 . The device of  claim 19 , where further comprising a light filter arranged in the housing an configured to suppress ambient light from the sensor.